The invention relates to fault tolerant digital data processing and, particularly, to apparatus and methods for providing fault tolerant communications with peripheral devices.
Faults in digital computer systems are inevitable and are due, at least in part, to the complexity of the circuits, the associated electromechanical devices, and the process control software. To permit system operation even after the occurrence of a fault, the art has developed a number of fault-tolerant designs. Among these is Rennels, "Architecture for Fault-Tolerant Spacecraft Computers," Proceedings of the I.E.E.E., Vol. 66, No. 10, pp. 1255-1268 (1975), disclosing a computer system having independent self-checking computer modules (SCCM's). In the event of failure of a module, the SCCM is taken off-line.
An improved fault-tolerant digital data processing system is currentlY available from the assignee hereof, Stratus Computer Company, of Marlboro, Massachusetts. This system employs redundant functional unit pairs, e.g., duplicative central processing units, duplicative memory units, and duplicative peripheral control units, interconnected for information transfer by a common system bus.
The aforementioned system bus includes two duplicative buses, the A Bus and the B Bus, as well as a control bus, the X Bus. During normal operation, signals transferred along the A Bus are duplicated through simultaneous transmission along the B Bus. Signals transferred along the X Bus, including timing, status, diagnostics and fault-responsive signals, and are not duplicated.
Within the Stratus System, control of and communications with periPheral devices are effected by peripheral control units One such unit, the communication control unit, routes control and data signals to attached peripheral devices by way of a communication bus.
With this background, an object of this invention is to provide an improved digital data processing system. More particularly, an object of this invention is to provide a system for improved fault-tolerant communication with, and control of, peripheral devices
A further object of this invention is to provide an improved fault-tolerant bus structure for use in digital data processing apparatus and, particularly, for use in communications with data processor peripheral units.
Yet another object of this invention is to provide an input/output controller for controlling and communicating with plural periPheral devices over a common peripheral bus structure.
Other objects of the invention are evident in the description which follows.